| Highly monodisperse polymer microspheres were synthesized by in-situ photopolymerization of microdroplets containing monomers and additives generated by a vibrating orifice aerosol generator (VOAG), and characterized by optical microscopy and scanning electron microscopy (SEM). Optimum reaction conditions of preparing monodisperse solid polymer particles (temperature, monomer concentration, tank pressure, vibrating frequency, and dispersion air) were obtained. The VOAG system was modified and improved so that microdroplets of various solutions may be produced within the range of optimum operation conditions. Many liquids, or solutions such as water, acetone, ethanol, Freon, monomer solutions, aqueous solutions, organic solutions and so on were comprehensively used in the system. Microdroplets with the diameter in the range of 5 to 100 ptm can be tuned and tailored according to variable purposes. Evaporation processes, properties, and characters of microdroplets such as changes in size and refractive index were studied through analyzing elastic and Raman scattering spectra collected from a linear stream of microdroplets. Raman spectra from microdroplets were obtained with a 9040 single monochromator. The resolution and accuracy of the monochromator was improved through an optical assembly that eliminates strong background light. Theoretical peaks of TE and TM modes were compared and matched well with experimental peaks from elastic and inelastic spectra. Mathematical models about evaporation of microdroplets involving volatile and nonvolatile components are used to explain experimental data. Fast mass and energy transport processes were studied in monodisperse microdroplets of Freon 113 and dibutyl phthalate (DBP). There exist the gradients of concentration, temperature, and refractive index inside microdroplets during the rapid processes of evaporation or growth. Raman spectra from microdroplets of aqueous solution of CO2 and carbonates were also studied to investigate fast reaction processes. |
